The present invention relates to a novel reinforcement member for flexible drive belts and, more particularly, to a novel reinforcement member and method of manufacturing timing belts. The present application is related to a co-pending application Ser. No. 724,604, filed in the name of the present inventor and assigned to the assignee of the present invention.
Timing belts are flexible drive belts, similar to pulley-type belts, which have teeth on one or more sides of the belt which permits the belt to perform much as gears perform in transmitting precise precision motion. Timing belts, also known as synchronous belts, generally do not transmit the amount of power that a gear will transmit, but offer light weight and alignment flexibility with the advantage of non-slip precision motion transmission. In such precision motion transmission, the motion is transmitted by the pulley teeth meshing with the belt teeth and during the meshing operation of the engagement and disengagement of the teeth, relative movements take place between the pulley teeth and the belt teeth. Accordingly, several prior art structures and compositions have been suggested for manufacturing belt structures which provide a high degree of flexibility while maintaining the necessary wear and life characteristics of the belt.
Belts for transmitting motion have been known for many years, as evidenced by U.S. Pat. Nos. 1,928,869, 1,611,829, 3,464,875 and 4,266,937 which describe processes in which the cogs or teeth are preformed in some manner and placed about a drum and then the remaining portion of the belt components or belt sleeve is wrapped around the teeth to form the completed uncured belt sleeve. More recently U.S. Pat. No. 4,487,814 describes a belt construction and the method of manufacture of the same.
Conventional timing belt constructions for industrial use, which include V-belts and drive belts constructions, are generally comprised of a polymeric matrix material, such as, rubber or polyurethane, and the like, reinforced with a higher strength material, primarily glass, fabric or an arumid, and with an even higher Young's modulus filament, primarily metal, so as to resist stretching and maintain precise belt-tooth spacing under operating load conditions. Moreover, such timing belts, containing glass or fabric reinforcements, generally do not possess sufficient Young's modulus coefficients to withstand stretching or elongation of the belt during operating loads. Thus, the preferred reinforcement is generally a metal, such as steel.
Although, timing belts comprised of rubber reinforced with metal filaments, such as steel cables and the like have been suggested, such belt structures present problems relating to corrosion of the metal within the belt, slipping and fatigue of the metal during operating load, adhesion problems with respect to the metal to the rubber reinforced belt construction and the difficulty of producing a belt construction possessing the necessary flexibility and stretch required in order to effectively utilize steel as a reinforcing member of the belt. The flexibility of the belt is necessary to prevent, during the operating load conditions of the belt motion transmitted from the pulley teeth meshing with the belt teeth, the engagement and disengagement of the pulley teeth and the belt teeth with respect to each other, which action results in substantial teeth wear in that portion of the belt construction.
Importantly, also, and perhaps the most important difficultly associated with the use of steel as the reinforcement tensile member within a belt construction relates to the difficulties associated with the use of steel in the method of manufacturing for timing belts. In general, timing or drive belts are manufactured by applying an inner rubber reinforced layer from a continuous sheet around a mandrel drum having an outer surface longitudinally grooved, which grooves provide the internal teeth molded structure in the timing belt construction. Thus, initially, a continuous layer of uncured rubber reinforced material is positioned and layed around the mandrel to form a tubular sleeve of material. Conventionally, a reinforcement cord or filament is then wrapped about the inner reinforced sheet of rubber continuously across down the length of the tubular sleeve. Next, an outer rubber protective layer is stitched and wrapped about the reinforcement cord or filament wrap and the resultant uncured long layered tube of rubber reinforced material is placed in a curing apparatus to cure the composite structure. Thereafter, cutting knives are positioned adjacent the sleeve to cut predetermined widths of the timing belts off of the formed and cured composite sleeve to produce the dimensioned timing belt, as desired. However, during the cutting operation of the layered and cured sleeve, the reinforcement material is cut and exposed at the sides of the cut belt. Such exposed steel ends behave poorly in use and cause difficulty during the cutting operations. Moreover, such structures permit corrosion and the tendency of the steel filament cord to move out of the side of the belt, to catch moving parts of the mechanical device. Such difficulties result in a timing belt construction which is unsatisfactory and a timing belt that possesses a short operating lifetime.
It follows that great manufacturing difficulties are introduced to overcome the above described deficiencies of having the reinforcement material emerge from the belt assembly sidewalls.
The above-described drawbacks and shortcomings of the prior art belt constructions and the conventional method of manufacturing timing belts and other types of V-belts or drive belts, and the secondary difficulties associated with the manufacture of such belt structures will be hereinafter described with reference to FIGS. 1-7.
As shown in FIG. 1, a cylindrical metal mold or mandrel 18 having longitudinally extending grooves 18a or teeth 19 on the outer surface thereof is provided as the former for the belt construction. In FIG. 2, a strip of uncured polymeric matrix material 20 is positioned about the outer surface of the metal mandrel 18 to provide the gear tooth engaging wear surface 14 portion of the prior art belt construction or assembly 30. The strip of polymeric matrix material 20 may be wrapped several times around the mandrel 18 to provide a wear and friction surface portion of a belt assembly and is comprised of a reinforcing fiber material 23 disposed substantially uniformly throughout the polymeric matrix material 20 to provide the gear-tooth wear surface portion 14 of the belt assembly 30. During manufacture, the application of the strip of polymeric matrix material 20 is sufficient to provide the desired buildup and thickness of the gear-tooth wear surface portion of the prior art belt assembly 30.
As shown in FIG. 3, the next step in the process for manufacturing a cog or tooth-type belt construction or assembly 30 is the positioning of the reinforcing cord or filament 24 about the strip of polymeric matrix material 20. Generally, as described in U.S. Pat. No. 3,188,254, the reinforcing cord 24 is spirally spun around the periphery of the strip of polymeric matrix material 20 and applied under high tension. The reinforcing cord 24 may be of such material such as nylon, rayon, polyester, glass fibers or steel and the application of the cord about the mandrel assists the polymeric matrix material 20 in flowing into the grooves 18a between the longitudinal teeth 19 of the mandrel 18.
After the reinforcing cord or filament 24 has been wound about the mandrel 18, as shown in FIG. 4, an additional sheet or cover layer 22 of a plastomeric or rubber material, of a type known to those skilled in the art, is positioned around the wound reinforcing cord and matrix material and stitched thereon to complete the raw uncured tubular sleeve of belting material. Thereafter, tubular sleeve and mandrel assembly is positioned in a conventional steam vulcanizing process, which is well known in the art, to complete the vulcanizing process of the belt assembly. During curing or vulcanization, there is additional flow of rubber or elastomeric material throughout the composite structure to provide a cured integral belt sleeve, the composite as shown in cross-section in FIG. 5. Thereafter, as shown in FIG. 6, the cured belt sleeve on the mandrel is removed from the curing mold and cut by knives 26 into individual belt constructions or assemblies 30, as shown in FIG. 7 and disclosed in U.S. Pat. No. 4,487,814. As shown in FIGS. 3 and 7, because the reinforcing cord or filament 24 is spirally wound about the mandrel, when the individual belts are cut from the cured sleeve, the cutting operation necessarily provides a plurality of areas on the cut side of the belt assembly 30 where the steel reinforcing cord or filament 24 is exposed along the side and at the ends, as shown by 28 in FIG. 7. These exposed ends permit corrosion within the belt assembly, which reduces operating lifetimes of the belt assembly 30, and permit the steel filament or other reinforcing cord to move out of the side of the belt to catch on the mechanical devices driving the drive belt.